Date: Tue, 07 Sep 2010 10:26:22 +0300 From: Andriy Gapon <avg@icyb.net.ua> To: Wiktor Niesiobedzki <bsd@vink.pl>, Pawel Jakub Dawidek <pjd@freebsd.org>, Konstantin Belousov <kib@freebsd.org> Cc: freebsd-fs@freebsd.org Subject: Re: zfs very poor performance compared to ufs due to lack of cache? Message-ID: <4C85E91E.1010602@icyb.net.ua> In-Reply-To: <AANLkTikNhsj5myhQCoPaNytUbpHtox1vg9AZm1N-OcMO@mail.gmail.com> References: <5DB6E7C798E44D33A05673F4B773405E@multiplay.co.uk> <AANLkTikNhsj5myhQCoPaNytUbpHtox1vg9AZm1N-OcMO@mail.gmail.com>
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on 06/09/2010 21:34 Wiktor Niesiobedzki said the following: > As far as I have check recently, nginx is using sendfile by default. > There is already a reported bug against ZFS+sendfile > (http://www.freebsd.org/cgi/query-pr.cgi?pr=141305&cat=) which results > in bad performance. > > The quickest workaround is to set: > sendfile off; > > In http {} sectio of nginx.conf. > > What I personally have observed, is that memory, that is used by > sendfile, once freed lands in Inact group. And ARC is not able to > force free of this memory. Well, there is a patch for this, but that's besides the point of the sendfile issue. > In my case, where I have 1G of ARC, then after sending 2G of file, my > ARC is barerly on minimum level, and my ARC hit ratio drops to ~50%. > > If I remove the file that was sent through sendfile, memory is moved > from Inact to free, from where ARC happly grabs what it wants, and ARC > hit ratio comes back to normal (~99%). Interesting. I briefly looked at the code in mappedread(), zfs_vnops.c, and I have a VM question. Shouldn't we mark the corresponding page bits as valid after reading data into the page? I specifically speak of the block that starts with the following line: } else if (m != NULL && uio->uio_segflg == UIO_NOCOPY) { I am taking mdstart_swap as an example and it does m->valid = VM_PAGE_BITS_ALL. -- Andriy Gapon
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